Those most likely to be affected will be the very young, the very poor and the very recently arrived – those, in other words, who are least likely to have alternative options.

I'm not altogether sure that Transport for London (TfL) has entirely thought through its plans to ban cash fares on its 7,500-odd buses. For most of us, most of the time, they’ll be marvellous. Just occasionally, though, it’s going to cause a bloody big headache. This would be bad enough, except that those most likely to be affected will be the very young, the very poor and the very recently arrived – those, in other words, who are least likely to have alternative options.

Once upon a time, pretty much all bus fares were bought on board the vehicle from a cheery sort in a hat. Today, though, except for the bored-looking cost-centres whose job it is to stop you falling out of the back of Boris buses, we don't bother with conductors any more. Most people use Oyster, TfL's automated ticketing system, either to show they've got a Travelcard or to pay as they go. There are other cards you can use to pay for your bus fares, too: bank cards fitted with the newfangled contactless payment systems. Today, TfL reckons, there are around 60,000 cash journeys made each day on its buses. That sounds like a lot, but it's only 1% of the total.

Forcing these stragglers to go cashless would have a number of advantages. It'd speed up boarding times (no more fiddling for small change). It'd cut crime (no point holding up a bus that doesn't carry money). It'd allow "operational flexibility" (no chance of working out what that even means).

It'd save TfL £24 million a year by 2019-20, it reckons, but it'd save passengers money too, because single fares are cheaper on Oyster than by cash. This is a bit of a cheat – TfL, after all, is the one that sets the bloody fares – but nonetheless, as things stand, you're better off paying for your bus through a medium that doesn’t have the Queen’s face on it.

Alongside all these advantages, though, the plan brings with it two obvious problems. One is relatively minor. The other isn’t.

One problem is that going cashless will confuse the hell out of anyone who doesn't live in London. Bus drivers will be lumbered with the unenviable task of explaining to tourists why they're not allowed on a large chunk of London's transport network without a strange lump of blue plastic. It’s a bit like hanging up a big sign reading, "London – open for business as soon as you've filled in the requisite form".

That, though, is the smaller problem. The bigger one concerns those who do use Oyster, but pay for their travel as they go. At some point, they’re going to run out of credit and need to top up, only to find they can't because it's the middle of the night and they're in Barking. TfL claims to have thought of this, and says it's considering letting you make one extra journey after you run out of credit. This is sweet of them, but ignores the fact you might have inadvertently used that journey to get you to Barking in the first place.

At that point, you’re dependent on one last safety net. TfL doesn’t tend to publicise this, but its drivers have discretionary powers to allow vulnerable people to travel for free. Exactly who this covers, though, is not entirely clear. A raucously drunk teenage girl is, by any sensible definition, vulnerable. They’re also exactly the kind of person you probably don’t want on your bus.

The upshot of all somebody, some time, is going to find themselves drunk, in the middle of nowhere, and unexpectedly unable to get home. A TfL spokesman told me this situation was “hypothetical”, which is fair comment, but given that there are 6 million bus journeys made every day in London, it’s nonetheless likely to happen quite a lot. Not all of the people thus affected will be burly men.

For most of us, none of this should be a problem. There are contactless payment cards. There's automatic top-up. Either of these will make it damned near impossible to get into this mess. But what both these solutions have in common is that they require you to have a bank account. Certain groups of people don’t generally have bank accounts. These include children, bankrupts and asylum seekers. These, of course, are exactly the people you want to leave dependent on the good will of a night bus driver.

No final decision has yet been made on this plan – TfL is consulting until 11 October – but it's hard to escape the feeling that this is one of those consultations that's softening us up for the inevitable, rather than genuinely asking what we think. The chair of TfL, after all, is one Boris Johnson, and since he became mayor single bus fares, most likely to be paid by the poor, have shot up by 50%. He’s also made it clear, through his expensive pseudo-Routemasters, that he sees buses less as a means of conveyance than as set decoration for a Richard Curtis movie. Another policy in which TfL privileges its own administrative convenience over the needs of those at the bottom of the pile would be rather in keeping.